1. Field of the Invention
The present invention is broadly concerned with improved compositions for the regeneration for cation exchange resins commonly used in household or industrial contexts for the softening of water. The compositions of the invention are generally of the type disclosed in U.S. Pat. No. 4,839,086, including respective amounts of citric acid and a salt of citric acid, but are improved by the addition of an agent for enhancing the iron sequestering capability thereof; this agent advantageously includes a quantity of a gluconic acid source or salt of gluconic acid.
2. Description of the Prior Art
Water softening systems have long been used in households and by industry to replace hardness cations such as calcium and magnesium with sodium ions. This is accomplished by passing an incoming water supply through a bed of sodium charged cation exchange resin beads or particles. As the water passes through the cation exchange resin bed, the incident hardness cations are exchanged for the sodium ions of the bed. In the course of time, the ion exchange resin bed becomes saturated with hardness cations removed from the incoming water, and it is necessary to recharge the bed by passing a brine solution primarily consisting of sodium chloride through the resin bed. This replenishes the bed with sodium ions and removes the unwanted calcium, magnesium, or other ions previously removed from the treated water.
Over time, the exchange capacity of an ion exchange resin bed deteriorates as impurities in the incoming water collect in the resin bed and are not removed by periodic recharging. At some point, depending primarily on the characteristics of the incoming water supply, the resin bed becomes unacceptably "fouled", i.e. the resin bed's capacity to soften water has been diminished to an extent that it must be specially treated to restore softening capacity.
Although a number of factors can lead to fouling of an ion exchange resin bed, perhaps the greatest single contributing factor is the presence of iron in an incoming water supply. Iron can exist in several valence states in water, the most common being the ferrous and ferric states. It is most desirable to maintain the iron in the ferrous state, inasmuch as ferrous iron can readily be removed during conventional resin bed regeneration. However, ferrous iron tends to become oxidized to the ferric state after being exchanged onto a resin bed, which the makes its removal very difficult and can cause the resin beads to split.
In the case of certain relatively high pH regenerating compositions, the resulting brine solutions are cloudy because of the presence of carbonates. In use, these carbonates can be effectively "filtered" by the resin beads thus lowering the bed efficiency and contributing to the need for frequent bed regeneration.
A number of prior compositions have been proposed for use as ion exchange resin bed regenerants. For example, U.S. Pat. No. 4,540,715 describes the use of a surfactant and an alkali metal citrate in a regenerating composition. Other prior systems have made use of citric acid as a sequestering agent for iron. These prior compositions have proven less than entirely satisfactory, however, principally because of their inability to properly control the iron problems described previously.
U.S. Pat. No. 4,839,086 represents a distinct breakthrough in the art and describes greatly improved regenerating compositions made up of, preferably, respective minor amounts of citric acid, a salt of citric acid (e.g., sodium citrate), and an anti-caking agent. Compositions in accordance with this patent can be mixed with a preponderant amount of sodium chloride to provide a greatly improved product for regeneration of cation exchange resins.